Description

1, University of Oxford, Oxford, , United Kingdom2, University of Oxford, Oxford, , United Kingdom

With the efficiency of perovskite photovoltaic cells rapidly improving, the Shockley-Queisser limit1 is not too far from reach. On approaching this limit, charge-carrier extraction will be limited only by radiative bimolecular recombination of electrons with holes.2 However, the fundamental physics behind this process, and its link with material stoichiometry, is still not understood. Here we show that bimolecular charge-carrier recombination in methylammonium lead triiodide perovskite can be fully explained as the inverse process of absorption. By carefully considering for contributions to the absorption from bound excitons and unbound electron-hole continuum states, with support from GW ab initio calculations3, we are able to determine bimolecular radiative recombination rate constants from absorption spectra. We show that the sharpening of photon, electron and hole distribution functions increases the bimolecular radiative rate by roughly an order of magnitude as the temperature is lowered from room temperature to 50K. Our findings thus give a fundamental understanding of the electronic processes in these hybrid perovskites, which will allow for guided exploration of alternative stoichiometries with desirable photovoltaic properties.